I also bought a .595" Lee round ball mould from Track several years ago. I don't know the current status of Lee's mould production, but I've always believed that if you want the truth, you go to the source. A call to Lee Precision may be the way to go.
I cast some balls, but I'm not averse to using precast or commercial swaged balls when convenient. There is no question that casting your own is cheaper, if you do a lot of shooting. For the occasional shootist, precast balls are not a bad deal.
Another manufacturer to consider would be Moose Moulds. I'm unable to post a link, but if you Google "moose moulds" (with the "u" in "mould"), a link to their website will pop right up. Look in their menu for "Moose Balls." They have a wide selection of sizes, including .595", but they also have a few that nobody else makes. I bought a .550" round ball mould from them and I'm pretty happy with it. I believe they make their moulds to order, and they gave me a choice of a tangential cut-off (like Lee) or with a sprue (like Lyman). It does not take them long to fill an order. They are good folks, with a family-run operation, and the proprietor is a competition black powder shooter. The one thing that may put people off is the price... $100 for a single cavity mould or $125 for a double cavity. You have to decide for yourself if that price is acceptable. It won't cost you anything to look at what they offer. I have no regrets with regard to the one I bought from them.
Good luck, brother! I hope you find your mould.
Notchy Bob